A woman wears a shirt stating her views on gay marriage outside City Hall in San Francisco in 2010. (Ben Margot/AP)

With this amicus brief, support in the GOP for same-sex marriage rights has jumped a generational divide. This is no longer an issue only for the under-40 generation. Same-sex marriage rights can now show support everywhere in the party, including its highest officeholders.

Among those who signed it: me.

I signed it as a longtime opponent of same-sex marriage, worried by exactly the arguments advanced by the Californians who passed Proposition 8 to stop it: that the spread of same-sex marriage would change the way men and women thought about marriage in ways that would discourage them from forming married families.

Since 2009, we have seen a sharp decline in this country in both marriage and childbearing. But that decline obviously has little or nothing to do with same-sex marriage. It has obviously everything to do with the economic crisis—and the long previous years of persistent decline in the wages and opportunities of Americans, especially young Americans.

As a conservative concerned with stabilizing families to rely less on government aid, I have been convinced: I've been worrying about the wrong thing. Stopping same-sex marriages does nothing to support families battered by economic adversity. Instead, it excludes and punishes people who seek only to live as conservatives would urge them to live. Treating same-sex partnerships differently from husband-wife marriages only serves to divide and antagonize those who ought to be working together.

Treating same-sex partnerships differently from husband-wife marriages only serves to divide and antagonize those who ought to be working together.

Like many signatories of the amicus brief, my thinking has been influenced by the fine example of the many committed, devoted same-sex couples I know. At least as much, however, I have also been swayed by an intensifying awareness of the harm culture-war politics has done to my party. Culture-war politics have isolated the GOP from the America of the present and future, fastening it to politics of nostalgia for a (mis)remembered past. Culture-war politics have substituted for relevant cultural policies aimed at encouraging the raising of children within married families. Worst of all, culture-war politics has taught the GOP to talk to America as if the nation were split into hostile halves, as if more separates Americans than unites them.

If the GOP should have learned one lesson from the last election, it was to stop talking about Americans in fractions and percentages, and to speak to America as one people. To stigmatize the aspirations of some Americans is to break faith with the ideals of all Americans—and to surrender hope of gaining the support of a majority of Americans.

The America of the future is rising all around us. It will be a different and often surprising country. It will be a country that judges personal relationships not by the chromosome pairing of any given couple, but by that couple's mutual commitment and shared responsibility. This is a future that Republicans should welcome—and are welcoming. It's why this amicus brief is gaining signatures every day and why the party of individual freedom can give voice to gay equality.